@article{gagnon_biswas_zhang_brown_wollenzien_mattos_maxwell_2012, title={Structurally Conserved Nop56/58 N-terminal Domain Facilitates Archaeal Box C/D Ribonucleoprotein-guided Methyltransferase Activity}, volume={287}, ISSN={["1083-351X"]}, DOI={10.1074/jbc.m111.323253}, abstractNote={Background: Box C/D RNPs direct site-specific 2′-O-methylation of rRNA. Results: The Nop56/58 and fibrillarin core proteins establish a very stable dimer with Nop56/58 contributing to methyltransferase activity. Conclusion: The Nop56/58 core protein plays a role not only in RNP assembly, but also methyltransferase activity. Significance: Our observations reveal a novel role for the Nop56/58 core protein in box C/D RNP function. Box C/D RNA-protein complexes (RNPs) guide the 2′-O-methylation of nucleotides in both archaeal and eukaryotic ribosomal RNAs. The archaeal box C/D and C′/D′ RNP subcomplexes are each assembled with three sRNP core proteins. The archaeal Nop56/58 core protein mediates crucial protein-protein interactions required for both sRNP assembly and the methyltransferase reaction by bridging the L7Ae and fibrillarin core proteins. The interaction of Methanocaldococcus jannaschii (Mj) Nop56/58 with the methyltransferase fibrillarin has been investigated using site-directed mutagenesis of specific amino acids in the N-terminal domain of Nop56/58 that interacts with fibrillarin. Extensive mutagenesis revealed an unusually strong Nop56/58-fibrillarin interaction. Only deletion of the NTD itself prevented dimerization with fibrillarin. The extreme stability of the Nop56/58-fibrillarin heterodimer was confirmed in both chemical and thermal denaturation analyses. However, mutations that did not affect Nop56/58 binding to fibrillarin or sRNP assembly nevertheless disrupted sRNP-guided nucleotide modification, revealing a role for Nop56/58 in methyltransferase activity. This conclusion was supported with the cross-linking of Nop56/58 to the target RNA substrate. The Mj Nop56/58 NTD was further characterized by solving its three-dimensional crystal structure to a resolution of 1.7 Å. Despite low primary sequence conservation among the archaeal Nop56/58 homologs, the overall structure of the archaeal NTD domain is very well conserved. In conclusion, the archaeal Nop56/58 NTD exhibits a conserved domain structure whose exceptionally stable interaction with fibrillarin plays a role in both RNP assembly and methyltransferase activity.}, number={23}, journal={JOURNAL OF BIOLOGICAL CHEMISTRY}, author={Gagnon, Keith T. and Biswas, Shyamasri and Zhang, Xinxin and Brown, Bernard A., II and Wollenzien, Paul and Mattos, Carla and Maxwell, E. Stuart}, year={2012}, month={Jun}, pages={19418–19428} }
 @article{biswas_buhrman_gagnon_mattos_brown_maxwell_2011, title={Comparative Analysis of the 15.5kD Box C/D snoRNP Core Protein in the Primitive Eukaryote Giardia lamblia Reveals Unique Structural and Functional Features}, volume={50}, ISSN={["0006-2960"]}, DOI={10.1021/bi1020474}, abstractNote={Box C/D ribonucleoproteins (RNP) guide the 2'-O-methylation of targeted nucleotides in archaeal and eukaryotic rRNAs. The archaeal L7Ae and eukaryotic 15.5kD box C/D RNP core protein homologues initiate RNP assembly by recognizing kink-turn (K-turn) motifs. The crystal structure of the 15.5kD core protein from the primitive eukaryote Giardia lamblia is described here to a resolution of 1.8 Å. The Giardia 15.5kD protein exhibits the typical α-β-α sandwich fold exhibited by both archaeal L7Ae and eukaryotic 15.5kD proteins. Characteristic of eukaryotic homologues, the Giardia 15.5kD protein binds the K-turn motif but not the variant K-loop motif. The highly conserved residues of loop 9, critical for RNA binding, also exhibit conformations similar to those of the human 15.5kD protein when bound to the K-turn motif. However, comparative sequence analysis indicated a distinct evolutionary position between Archaea and Eukarya. Indeed, assessment of the Giardia 15.5kD protein in denaturing experiments demonstrated an intermediate stability in protein structure when compared with that of the eukaryotic mouse 15.5kD and archaeal Methanocaldococcus jannaschii L7Ae proteins. Most notable was the ability of the Giardia 15.5kD protein to assemble in vitro a catalytically active chimeric box C/D RNP utilizing the archaeal M. jannaschii Nop56/58 and fibrillarin core proteins. In contrast, a catalytically competent chimeric RNP could not be assembled using the mouse 15.5kD protein. Collectively, these analyses suggest that the G. lamblia 15.5kD protein occupies a unique position in the evolution of this box C/D RNP core protein retaining structural and functional features characteristic of both archaeal L7Ae and higher eukaryotic 15.5kD homologues.}, number={14}, journal={BIOCHEMISTRY}, author={Biswas, Shyamasri and Buhrman, Greg and Gagnon, Keith and Mattos, Carla and Brown, Bernard A., II and Maxwell, E. Stuart}, year={2011}, month={Apr}, pages={2907–2918} }
 @article{gagnon_zhang_qu_biswas_suryadi_brown_maxwell_2010, title={Signature amino acids enable the archaeal L7Ae box C/D RNP core protein to recognize and bind the K-loop RNA motif}, volume={16}, ISSN={["1469-9001"]}, DOI={10.1261/rna.1692310}, abstractNote={The archaeal L7Ae and eukaryotic 15.5kD protein homologs are members of the L7Ae/15.5kD protein family that characteristically recognize K-turn motifs found in both archaeal and eukaryotic RNAs. In Archaea, the L7Ae protein uniquely binds the K-loop motif found in box C/D and H/ACA sRNAs, whereas the eukaryotic 15.5kD homolog is unable to recognize this variant K-turn RNA. Comparative sequence and structural analyses, coupled with amino acid replacement experiments, have demonstrated that five amino acids enable the archaeal L7Ae core protein to recognize and bind the K-loop motif. These signature residues are highly conserved in the archaeal L7Ae and eukaryotic 15.5kD homologs, but differ between the two domains of life. Interestingly, loss of K-loop binding by archaeal L7Ae does not disrupt C′/D′ RNP formation or RNA-guided nucleotide modification. L7Ae is still incorporated into the C′/D′ RNP despite its inability to bind the K-loop, thus indicating the importance of protein–protein interactions for RNP assembly and function. Finally, these five signature amino acids are distinct for each of the L7Ae/L30 family members, suggesting an evolutionary continuum of these RNA-binding proteins for recognition of the various K-turn motifs contained in their cognate RNAs.}, number={1}, journal={RNA}, author={Gagnon, Keith T. and Zhang, Xinxin and Qu, Guosheng and Biswas, Shyamasri and Suryadi, Jimmy and Brown, Bernard A., II and Maxwell, E. Stuart}, year={2010}, month={Jan}, pages={79–90} }